The present invention relates, in general, to the air distribution units and, more particularly, relates to ceiling mounted, thermally-powered, linear, change-over diffusers for use in air conditioning systems.
The use of air distribution units or diffusers as part of an air conditioning system for large structures is widespread. Such systems typically include a plurality of ceiling mounted diffusers which are supplied from a central source with either hot or cold air, depending upon temperature within the structure as sensed by control apparatus. One type of diffuser which is commonly employed is the linear diffuser which can be mounted proximate the perimeter walls or periphery of the space being heated or cooled.
Whether linear or non-linear diffusers are employed, it is well known that the most effective manner distributing air from diffusers during cooling is to direct the air in a horizontal flow across the ceiling of the room by employing what is known in the industry as the "Coanda effect". A stream of air discharged from a diffuser at an angle less than about 35 to about 40 degrees with respect to the ceiling will tend to create a partial vacuum and cause the air stream to remain in contact with or hug the ceiling as a result of the Coanda effect. Cool air, therefore, can be distributed over a substantial area of the ceiling by employing the Coanda effect before the cool air begins to sink down into the room to cool the entire volume of the room. By contrast, best efficiency in connection with the distribution of hot air from a perimeter diffuser is for the air to be discharged in a generally vertically oriented stream which is detached from the ceiling and oriented for flow of the warm air downwardly over the walls and windows of the structure. Additionally, it is also well known that in well insulated buildings in most climates the volume of warm air needed to raise the temperature in a structure is usually less than the volume of cool air flow required during cooling.
Diffusers or air distribution units have been previously developed which include movable blades, vanes or bladders which allow modulation and/or off-on control of air supplied through the diffuser. Such prior art diffusers have been thermally powered, for example as is disclosed in U.S. Pat. No. Re. 30,953. The diffuser of U.S. Pat. No. Re. 30,953 employs a movable louvre or blade system in which the blades are moved across a discharge outlet by a thermally powered actutator of the type commonly used in automotive applications. U.S. Pat. Nos. 3,117,723 and 3,143,292, by contrast, disclose air distribution units in which a bladder is used to control volume discharged from the diffuser by a pneumatic controller. In each case, the above referenced prior art air distribution apparatus employs discharge outlet and control vanes or bladders which produce air flow in substantially the same direction, namely, along the ceiling of the structure being air conditioned. While air flow volume is modulated by such apparatus, no attempt has been made to vary the direction of air flow.